I need help with throwing an exception for the challenge, I cannot figure out what I am doing wrong.

Question

it keeps saying not to change the lapsDriven or barCount fields but I am not.

GoKart.java

class GoKart {
  public static final int MAX_BARS = 8;
  private String color;
  private int barCount;
  private int lapsDriven;

  public GoKart(String color) {
    this.color = color;
  }

  public String getColor() {
    return color;
  }
  public void charge() {
    barCount = MAX_BARS;
  }

  public boolean isBatteryEmpty() {
    return barCount == 0;
  }

  public boolean isFullyCharged() {
    return MAX_BARS == barCount;
  }

  public void drive() {
    drive(1);
  }

  public void drive(int laps) {
    lapsDriven += laps;
    barCount -= laps;
    if (barCount < laps) {
      throw  new IllegalArgumentException("!!!");
    }

  }
}

Answer 1 · 2017-09-26T00:05:36Z

September 26, 2017 12:05am

It tells you that you should throw the exception before lapsDriven and barCount is changed. If you look at the drive method you'll see that the first two lines do indeed change those variables:

public void drive(int laps) {
  lapsDriven += laps; // This increases lapsDriven
  barCount -= laps; // This decreases barCount
  if (barCount < laps) {
    throw new IllegalArgumentException("!!!");
  }
}

Which means that to throw the exception before those variables change, you have to place your code at the top of the method. Like this:

public void drive(int laps) {
  if (barCount < laps) {
    throw new IllegalArgumentException("!!!");
  }
  lapsDriven += laps;
  barCount -= laps;
}

If you don't then lapsDriven and barCount would be changed even if there is not enough bars for a lap, which would defeat the point of throwing the exception.

Edit: Changed some of my wording.

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Tim Blacquier

Tim Blacquier

I need help with throwing an exception for the challenge, I cannot figure out what I am doing wrong.

1 Answer

andren

andren